36 ELEMENTS OF SYLVICULTURE. 



has thus to be repeated several times until the object 

 in view is attained. 



Along with these rapidly growing and inferior trees 

 it is indispensable also to get rid of clumps of shoots 

 which may appear on some of the larger stools. 



These shoots, which seldom hold out any promise 

 in themselves, have at first a rapid growth, spread 

 out wide, and destroy all the seedlings around them 

 only to leave gaps in their place later on. 



In making cleanings, the mistake has often been 

 committed of removing at a single operation all soft- 

 wooded trees, and birches. This procedure is too 

 sweeping in its action. The birch and aspen are in 

 great demand for certain purposes ; the cover of soli- 

 tary trees of these two kinds is too slight to do any 

 real damage, and their wholesale extraction consider- 

 ably reduces the money value of young crops. 



THINNINGS. Thinnings now step in and shorten 

 the duration of the struggle between the individual 

 trees of the crop. At first they are still in the nature 

 of cleanings, inasmuch as they complete what the 

 latter began, i.e., the maintenance of the valuable 

 kinds ; afterwards their principal object is constantly 

 to improve the growth of the more promising trees. 

 We are thus led to distinguish the first thinnings 

 from thinnings properly so called, which are made 

 periodically, and for this reason are termed periodical 

 thinnings. 



Since the only way to improve the growth of the 

 crop is to favour the gradual development of the 

 crowns by setting them free, we may define a 

 thinning as an operation in which we open out the 



